This invention relates to methods and apparatus for inspecting workpieces such as substrates used to make magnetic disks or magnetic disks during any point in the manufacturing process (including the finished disk).
Magnetic disks are typically manufactured using the following method.    1. A disk-shaped substrate (typically an Al alloy) is lapped or ground.    2. A material such as a nickel phosphorus alloy is plated onto the substrate.    3. The plated substrate is polished and textured. (During texturing, texture grooves are typically formed in the substrate by mechanical abrasion to cause a subsequently deposited magnetic layer to exhibit anisotropy. It is also known to laser texture substrates for tribological reasons.)    4. One or more underlayers, one or more magnetic layers and one or more protective overcoats are deposited onto the plated substrate. (The deposition process can comprise sputtering or other techniques.) Other layers can also be deposited onto the substrate during manufacturing.    5. A lubricant is applied to the disk.
At various points during manufacturing (e.g. before or after texturing), it is desirable to inspect the substrate for bumps, pits, contaminant particles, or other defects. During such inspection, one should be able to detect very small defects. It is known in the art to use optical testers comprising lasers for scanning such substrates for this purpose. See, for example, U.S. Pat. Nos. 6,566,674 and 6,548,821, issued to Treves et al. (The Treves patents are incorporated herein by reference.) The testers also include a spindle for rotating the substrates, optical elements such as lenses through which the laser beam passes, and detectors for receiving laser light reflected by the substrates.
Testers are typically incorporated into test cells including a robotic arm for taking a substrate from a conveyor and placing the substrate in the tester, and for taking the substrate from the tester and placing it either back on the conveyor (e.g. if the substrate passes certain test criteria) or in one of several bins. Placement in the various bins depends upon what type of defect is present on a substrate surface. The substrates placed in these bins are re-worked, further evaluated, or thrown out.
The cell includes a safety enclosure, e.g. so that manufacturing personnel are not struck and injured by the robotic arm. In this prior art cell, when a bin is full, the entire test head shuts down so that the enclosure can be opened and the full bin can be replaced with an empty bin. This wastes production time. It would be desirable to reduce such a waste of time.